This invention relates to a face seal for preventing fluid leakage past a rotating shaft, and more particularly to such a seal which can be disassembled for service and repair without removing the entire seal assembly from the machine.
Many powered or power driven machines have a rotating shaft projecting through a bore in the machine casing for transmission of power and require a shaft seal to prevent leakage of lunbricant or working fluid around the shaft through the bore in the casing. One of the most effective seals is a face seal.
A face seal has two seal elements: a nonrotating seal nose held within a seal housing seated in a counterbore in the machine casing, and a mating ring fixed to and rotating with the shaft. An essential characteristic of a proper seal is continuous full circumferential contact between the seal nose and the mating ring during all conditions of use. Continuous 360.degree. contact requires two conditions. One is that the sealing surfaces on the seal nose and the mating ring be precise corresponding surfaces of revolution, preferably flat. The other condition is that the seal nose be flexibly mounted within its housing to enable it to follow the slight nutating motion of the mating ring on the shaft caused by slight misalignment of the mating ring on the shaft and slight misalignment of the shaft in its bearings.
The flatness of the seal nose and the mating ring is achieved by precision manufacturing techniques. The flexible mounting of the seal nose in the housing is accomplished by the use of a spring between the seal nose and the floor of the housing which biases the seal nose against the mating ring and allows the nutating motion as the seal nose follows the mating ring. An O-ring is disposed between the seal nose and the housing to prevent leakage of fluid through the housing around the seal nose.
When the machine is in operation, the mating ring holds the seal nose within the housing so there is no need for a mechanism to do this job. However, when the machine is being assembled, it is very desirable that the seal assembly be a single unit so that it can be inventoried and handled conveniently and so that there is no chance that the workers who assemble the machine itself assemble the seal improperly. Therefore, it is common practice to crimp or roll the top edge of the seal housing over a shoulder on the seal nose to hold the assembly together.
Permanent assembly techniques such as rolling or crimping the top edge of the seal housing over have two disadvantages. One is that the spring which urges the seal nose outwardly into contact with a mating ring tends to seal the seal nose against the rolled over flange on the seal housing to limit oil circulation and prevent oil from draining out of the seal housing when the machine is shut down. Puddles of oil which cannot drain from the seal housing can be heated to coking or varnish temperature by heat soak-back during the initial period after the machine is shut down and this varnish or coking of the oil can interfere with the free motion of the seal nose within the seal housing. The other disadvantage of a permanent assembly of the seal is that any inspection or repair of the seal assembly is rendered virtually impossible and requires instead the removal and replacement of the entire seal assembly.
Several prior art attempts have been made at providing a seal which can be disassembled for inspection and replacement of the spring, O-ring and seal nose. One technique uses a ring which fits into the seal housing and has two depending legs with radial projections which snap into diametrically opposed holes in the housing walls. This technique has the disadvantages that the external wall of the seal housing has a pair of holes through it which could cut the O-ring which is frequently used to seal the seal housing within the machine casing. In addition, this technique still requires the removal of the entire seal assembly in order to get access to the outside of the holes to disengage the projections on the legs of the retaining ring from the holes so that the retaining ring can be removed.
One other technique which has proven to be quite successful and is in wide use is the use of formed tangs on the antirotation channels which are fastened to the housing wall and lie in notches in the seal nose outer periphery. The tangs extend over the edge of the shoulder on the seal nose when the seal nose is inserted into the housing and rotated slightly so that one of the tangs extends over the edge of the notch. This technique works extremely well but does depend on the friction of the O-ring between the seal nose and to hold the seal nose in its locked position. Conceivably, during assembly operations of the machine the seal nose could become partially rotated within the housing and could be partially or completely released. Then when the shaft is assembled to the seal with the seal nose cocked or displaced from the seal housing, the seal nose could be broken or jammed into the housing in an inoperative position. This is an extremely unlikely condition, but in some situations it is worth the extra cost to provide a seal which eliminates even this remote possibility.